Trail of Fire?

Okay, so I'm trying to figure out this movement system for a project I'm working on. The idea is that after the player (the black square) moves away from the unit they are on, it catches fire–you can only move one unit per key click. The gif demonstrates what it kinda supposed to look like (it just came out really fast).

I've somewhat figured out a system to do this; there is a layer of white squares that are triggers and a layer of red squares that each get turned on once the player leaves their respective trigger. I would be fine with this except that means I have 162 gameobjects to load in each scene minimum (9x9), and ngl it doesnt quite look all that professional in transition from square to square.

I thought I might be able to make this work with tilemap colliders but the fire layer would only turn on after leaving the tile map as a whole (wont turn on til character is on the grey)

My question is is there a more elegant way to do this that I just am not seeing?